JP2001233667A - Manganese-zinc-based ferrite for power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an MnZn-based ferrite for a power supply suitable for applying to a switching power supply and having both low loss and a high strength. SOLUTION: This ferrite has a composition obtained by including at least one kind selected from 0.0050-0.1000 mass % of Ta2O5, 0.0100-0.1500 mass % of ZrO2, 0.0050-0.0500 mass % of Nb2O5 and 0.0050-0.0500 mass % of HfO2 with 0.0050-0.0200 mass % of Bi2O3, 0.0050-0.0500 mass % of SiO2 and 0.0200-0.2000 mass % of CaO in a basic component composed of 10.0-15.0 mol% of ZnO, 52.0-54.0 mol % of Fe2O3 and a residual amount of MnO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, low-loss MnZn ferrite for a power supply, which is suitable as a magnetic core material for a switching power supply transformer or the like.

[0002]

2. Description of the Related Art Oxide magnetic materials are collectively referred to as ferrites. These ferrites are further classified into hard magnetic materials such as Ba ferrite and Sr ferrite and soft magnetic materials such as MnZn ferrite and NiZn ferrite. A soft magnetic material is a material that sufficiently magnetizes even a very small magnetic field, and is used in a wide range of fields such as power supplies, communication devices, measurement and control devices, magnetic recording, and computers. And the characteristics required for such a soft magnetic material include:
Examples include low coercivity, high magnetic permeability, high saturation magnetic flux density, and low loss.

As a soft magnetic material other than oxide ferrite, there is a metal-based soft magnetic material. This metallic soft magnetic material has a high saturation magnetic flux density and is therefore advantageous compared to this point oxide type.On the other hand, however, it has a low electric resistance, so when it is used in a high frequency range, the loss due to eddy currents occurs. (Magnetic loss) increases. Particularly in recent years, electronic equipment has become smaller and smaller.
Due to the demand for higher density, the operating frequency has been increasing, and in the frequency band of about 100 kHz used for switching power supplies, the resistance of conventional metallic materials is low,
It is almost impossible to use it because heat generation due to eddy current loss increases. From such a background, MnZn-based ferrite is mainly used as a magnetic core material of a power transformer used in a high frequency band.

[0004] By the way, as a core material of a power supply transformer,
Especially for power-supply MnZn-based ferrites
Low loss is required. For low loss of magnetic material
As a factor controlling the loss, the magnetic anisotropy constant K
₁ In addition, the magnetostriction constant λ is known, and MnZn ferrite
These parameters also minimize the loss
MnO-ZnO-Fe_TwoO_Three The ternary composition has been
Has been selected.

In other words, the composition region where the loss is small is defined by the operating temperature (around 80 ° C.) of the power transformer.
This is a ternary composition region in which both the magnetic anisotropy constant K ₁ and the saturation magnetostriction constant λs are small. Further, the loss of the MnZn-based ferrite has a large temperature dependence, and the loss decreases as the temperature increases from room temperature, and starts to increase after the minimum temperature. Even when the operating temperature of the power transformer is 50 to 80 ° C., the temperature of the transformer can often be close to 100 ° C. due to a rise in the temperature of surrounding electronic components and the use environment temperature. Considering these conditions and considering the temperature dependence of the loss of MnZn-based ferrite, the material design of the current transformer core material is such that the temperature at which the loss is minimized is around 90-100 ° C. Have been.

The magnetic anisotropy constant K ₁ and the magnetostriction constant λ are determined by the main composition, and these influence the loss. In the case of the MnZn-based ferrite, the loss varies depending on a small amount of added components. That is, the total loss can be reduced by improving the density of the sintered body, increasing the grain boundary resistance, and increasing the specific resistance of the entire sintered body to reduce the eddy current loss. For example, as disclosed in JP-A-58-15037 and JP-A-3-184307, there are additive components that can reduce the loss by adding a small amount of about several hundred ppm.

[0007]

[SUMMARY OF THE INVENTION However, depending on the composition of MnO-ZnO-Fe ₂ O ₃ ternary MnZn ferrite, as we increase the amount of such additional components, the bending of the sintered body Strength such as strength and bending strength was significantly reduced, chipping occurred during processing, and cracks sometimes occurred when finally manufactured as products, or when incorporated into other electronic components as electronic components with other electronic components .
SUMMARY OF THE INVENTION The present invention advantageously solves the above problems, and has as its object to propose a low-loss, high-strength MnZn-based ferrite for power supply suitable for application to a switching power supply.

[0008]

SUMMARY OF THE INVENTION Now, the inventors have found that in order to solve the problems described above, a result of extensive studies about the effects on the sintered body strength additive components, the Bi ₂ O ₃ It has been found that the strength can be effectively improved by adding them together with little change in the loss value. The present invention is based on the above findings.

Accordingly, the present invention is, in the basic component comprising a component composition _{below, Bi 2 O 3: 0.0050~0.0200mass%} , SiO 2
: 0.0050 to 0.0500 mass% and CaO: 0.0200 to 0.20
Ta ₂ O ₅ : 0.0050-0.1000 mass%, ZrO ₂ together with 00 mass%
: 0.0100 ~ 0.1500mass%, Nb ₂ O ₅ : 0.0050 ~ 0.0500ma
ss% and HfO _2: a power source for MnZn ferrite which is characterized in that is contains at least one selected from among 0.0050~0.0500mass%.

In the MnZn ferrite of the present invention, 100 × 10
A bending strength of ⁶ N / m ² or more can be obtained. In the MnZn-based ferrite of the present invention, the temperature at which the loss is minimized is in the range of 80 to 120 ° C.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the reason why the composition of the MnZn-based ferrite in the present invention is limited to the above range will be described. First, the basic component composition was changed to ZnO: 10.0 to 15.0.
_{mol%, Fe 2 O 3:} 52.0~54.0 mol%, MnO: explained reasons for limiting the range of the balance. As described above, the magnetic properties required for power ferrites include high saturation magnetic flux density, high Curie temperature, and low loss. Of these, the saturation magnetic flux density and Curie temperature are the basic components. Is substantially determined by the mixing ratio of MnO, ZnO and Fe ₂ O ₃ . That is, in a region where the amount of ZnO is small, the saturation magnetic flux density increases with an increase in the amount of ZnO, but at the same time, the Curie temperature decreases. As the ZnO content further increases, the saturation magnetic flux density decreases. Even for the same MnZn-based ferrite material, if the material aimed at high magnetic permeability, increase the ZnO content and select a composition around 20 mol%, which is a component composition with small saturation magnetostriction, at the expense of saturation magnetic flux density. Even so, the composition has a high magnetic permeability. Here, in this composition having a large amount of ZnO, the density of the sintered body is high and there is no problem in the strength.
The amount of O is in the range of 15 mol% or less. Conversely, considering the loss in the temperature range of 80 to 120 ° C., a composition having a small amount of ZnO is more advantageous, but if the amount of ZnO is less than 10 mol%, the loss is rather increased. Therefore, the amount of ZnO is 10 mol%
As described above, the range is set to 15 mol% or less. More preferably 10 m
ol% or more and 14 mol% or less.

The temperature at which the loss is minimized also depends on the basic components as described above. The temperature at which the loss is minimized is
In order to maintain the temperature in the range of 80 to 120 ° C., about 54.0 mol% of Fe ₂ O _{3 and} 10 mol% of ZnO:
The content of Fe ₂ O ₃ is about 52.0 mol%, and if it falls outside this composition range, the loss value in the temperature range of 80 to 120 ° C. increases. Therefore, the amount of Fe ₂ O ₃ is in the range of 52.0 mol% to 54.0 mol%,
The balance was MnO. More preferable Fe ₂ O ₃ amount is 5
2.5 to 53.8 mol%.

The basic components have been described above. Next, additional components will be described. First, the inclusion of SiO ₂ and CaO is indispensable for improving sinterability and increasing the resistance of the grain boundary phase to achieve low loss. That is, SiO ₂
It has the effect of promoting sintering, and it is necessary to contain 0.0050 mass% or more in order to bring out this effect. However, if it is too much, abnormal grain growth occurs, so the upper limit was made 0.0500 mass%. However, when the content is near the upper limit, it is necessary to take measures such as lowering the sintering temperature. Further, when the content is relatively large, it is difficult to control the optimal grain boundaries, so preferably 0.00
It is contained in the range of 50 to 0.0350 mass%.

Although CaO has the effect of increasing the resistance of the grain boundaries together with SiO ₂ to reduce the loss, the content of CaO is 0.0200 ma.
If the content is less than ss%, the effect is poor, while if it exceeds 0.2000 mass%, there is a problem in sinterability.
It was contained in the range of 2000 mass%. Note that SiO ₂
When the amount is small, the CaO amount is preferably contained in the range of 0.0200 to 0.1250 mass%.

Furthermore, by adding a small amount of Ta ₂ O ₅ , ZrO ₂ , Nb ₂ O ₅ , HfO _2, etc. which do not form a spinel, a high-performance MnZn ferrite for power supply with little loss can be obtained. be able to. However, according to the investigation by the inventors, it has been clarified that the strength decreases with an increase in the content, and that the strength reduction is determined by the content regardless of the type of the additive component.

The reason for this is that the observation of the fractured surface where chipping or cracking has occurred is not due to insufficient sintering because there are more cracks in the grains than in the grain boundaries.
This is considered to be due to stress being applied to the crystal grains. That is, it is considered that these added components have an effect of increasing the grain boundary resistance, but at the same time, generate stress on the crystal grains. However, even those containing these additional components can reduce their stress depending on the firing conditions. For example, in the early stage of sintering to advance sintering, take time to raise the temperature and delay the cooling rate after sintering to reduce grain boundary segregation of added components and minimize strain on crystal grains. Can be. However, in that case, the firing time becomes long, which is not preferable in an actual production process from the viewpoint of efficiency.

Therefore, the present inventors have conducted intensive studies on this point, and as a result, it is extremely effective to solve the problem by including Bi ₂ O ₃ together with the above-mentioned element for increasing the grain boundary resistance. I found something. Thus, it is the greatest feature of the present invention to contain Bi ₂ O ₃ in combination with the element that increases the grain boundary resistance, and thus an advantageous improvement in strength is achieved without increasing loss. It is. However, Bi ₂ O ₃ content is too small, no strength improving effect, since it leads to a sharp increase in loss caused too much when abnormal grain growth Conversely, Bi ₂ O ₃ amount
The content was set in the range of 0.0050 to 0.0200 mass%.

The proper contents of the various components for improving the grain boundary resistance described above are as follows. Ta ₂ O ₅ is Si
It effectively contributes to an increase in specific resistance in the presence of O ₂ and CaO. However, if the content is less than 0.0050 mass%, the effect of its addition is poor. On the other hand, if the content exceeds 0.1000 mass%, loss increases. . Therefore, Ta ₂ O ₅ is assumed to be contained in the range of 0.0050~0.1000mass%. A more preferred range is from 0.0100 to
0.0800 mass%. ZrO ₂ is, like Ta ₂ O ₅ , SiO ₂ , Ca
In the coexistence with O, the resistance of the grain boundary is increased, which effectively contributes to the reduction of loss in a high frequency range. Although the ratio of the increase in resistance is somewhat lower than that of Ta ₂ O ₅ , the contribution of the loss reduction is large, particularly from the minimum temperature to the high temperature side. Here, poor in its effect ZrO ₂ content is less than 0.0100Mass%, whereas when it exceeds 0.1500Mass% reduces the effect of increasing the specific resistance Conversely, since loss increases, ZrO ₂ amount 0.0100
It was in the range of 0.1500 mass%. More preferably, 0.0100
It is in the range of ~ 0.1000 mass%. Nb ₂ O ₅ forms a grain boundary phase with SiO ₂ and CaO, increases grain boundary resistance and effectively contributes to loss reduction. However, poor its effect is less than the content 0.0050 mass%, whereas when it exceeds 0.0500Mass% excess precipitated in the grain boundary phase, so rather causes an increase in losses, Nb ₂ O
_The amount of ₅ was limited to the range of 0.0050 to 0.0500 mass%. The most remarkable effect is obtained in the range of 0.0500 to 0.0250 mass%. HfO ₂ has the function of increasing the grain boundary resistance, like ZrO ₂ . However, if the amount is too small, the loss improving effect is poor, while if the amount is too large, the loss increases.
The range was limited to 0500 mass%. Since it is a relatively expensive element, it is preferable to add it in the range of 0.0050 to 0.0300 mass%. Since the MnZn-based ferrite of the present invention has low loss, it is most suitable for a power supply.

[0019]

EXAMPLES Example 1 After the raw materials of the basic components were finally blended so as to have the composition shown in Table 1, wet mixing was performed using a ball mill for 16 hours, and then dried. This mixed powder was calcined in an air atmosphere at 970 ° C. for 2 hours. Then, SiO ₂ , CaC 0 ₃ , Bi ₂ O ₃ , Ta ₂ O ₅ and HfO ₂ were added to the calcined powder, SiO ₂ : 0.08 mass%, CaC 0 ₃ : 0.13 mass%, Bi ₂ O, respectively.
_{3: 0.0150mass%, Ta 2 O} 5: 0.04mass% and HfO _2: 0.
It was added so as to have a concentration of 02 mass%, wet-mixed and pulverized again using a ball mill, and then dried. 5 mass% to this powder
After adding 10% by mass of an aqueous solution of polyvinyl alcohol, the mixture is granulated and then molded into a rectangular parallelepiped having an outer diameter of 36 mm, an inner diameter of 24 mm, a height of 12 mm and a length of 60 mm, a width of 12 mm and a thickness of 6 mm. Then, firing was performed at 1330 ° C. for 3 hours in a nitrogen / air mixed gas atmosphere in which the oxygen partial pressure was controlled. At this time, the entire baking time was 10 hours.

[0020]

[Table 1]

The sintered ring sample thus obtained is wound (primary side: 5 windings, secondary side: 5 windings) under the following conditions: frequency: 100 kHz, maximum magnetic flux density: 200 mT. The loss below was measured by an AC BH tracer over a temperature range of 0-120 ° C. Figure 1 shows the change in loss with temperature
Shown in The rectangular parallelepiped sample has a length of 50 mm, a width of 10 mm,
A rectangular parallelepiped having a thickness of 5 mm was processed and subjected to a three-point bending test defined in JIS C 2561. FIG. 2 shows the results of the strength test in relation to the amount of ZnO. In addition, for comparison, the results of the measurement of the strength of a rectangular parallelepiped sample manufactured with the above-described composition excluding only Bi ₂ O ₃ are also shown.

As is evident from FIG. 1, all of the components satisfying the component composition range of the present invention have a minimum loss at about 90 ° C., and their absolute values are also small. Further, as shown in FIG. 2, although the strength changes with an increase in ZnO, those in the composition range of the present invention obtained sufficiently high strength in an appropriate ZnO amount range, Bi ₂ O
_The composition excluding ₃ has insufficient strength.

Example 2 ZnO: Fe ₂ O ₃ : MnO was 11.7: 52.9: 35.4 as the final composition.
A calcined powder was prepared in the same manner as in Example 1 with respect to the main component composition adjusted to have a molar ratio of, and various oxides shown in Table 2 were added thereto. Was calcined at a temperature of 1200 to 1350 ° C. for 2 to 6 hours in a mixed gas of nitrogen and air. The sintered body sample thus obtained was wound in the same manner as in Example 1, and the frequency: 100 k
Hz, the maximum magnetic flux density: The loss under the condition of 200 mT was measured. Table 2 shows the loss value Pcv at 90 ° C. Further, a three-point bending strength test was performed on the rectangular parallelepiped sintered body sample in the same manner as in Example 1, and the strength σ _3b is also shown in Table 2.

[0024]

[Table 2]

As is evident from Table 2, those satisfying the component composition range of the present invention have low loss,
The strength is also 100 × 10 ⁶ N / m ² or more due to the effect of adding Bi ₂ O ₃ .

[0026]

Thus, according to the present invention, a low-loss and high-strength MnZn ferrite for a power supply suitable for a magnetic core material such as a switching power supply transformer can be stably obtained, and its industrial value is extremely high. large.

[Brief description of the drawings]

FIG. 1 is a graph showing a loss under a condition of a frequency: 100 kHz and a maximum magnetic flux density: 200 mT, using a measured temperature as a parameter.

FIG. 2 is a graph showing the relationship between the three-point bending strength and the amount of ZnO in MnZn ferrite.

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Claims (1)

[Claims] 1. A basic component comprising a component composition _{below, Bi 2 O 3: 0.0050~0.0200mass%} , SiO 2: 0.0050~0.0500mass% and CaO: with 0.0200~0.2000mass%, Ta ₂ O _{5: 0.0050~0.1000mass%, ZrO 2: 0.0100~0.1500mass%} , Nb 2 O 5: 0.0050~0.0500mass% and HfO _2: characterized that it contained at least one selected from among 0.0050～0.0500Mass% MnZn ferrite for power supply.